Pseudorabies, also called Aujeszky's disease, is an acute infectious disease caused by Suid herpesvirus 1 (SuHV1) belonging to the Alphaherpesvirinae subfamily for many kinds of livestock such as swine, cattle and sheep, as well as poultry and wild animals, with the main symptoms of fever, intense itching (except swine) and encephalomyelitis. Pseudorabies in swine is found nationwide in China causing severe damages, and is one of the major diseases limiting the large-scale production of pig farms. Infection can result in abortion, stillborn or mummified fetuses in pregnant sows, and neurological signs, paralysis and a high death rate in piglets. Pseudorabies virus (PRV) with strong pantropic properties, neurotropic properties and latent infectivity, may establish long-term latent infection in the peripheral nervous system, and then the latently infected host starts to get sick when the latent virus is activated into the infectious virus.
According to recent researches, there are reports of new features of pseudorabies, of which the significant manifestations include that infection among swine at any ages, horizontal transmission among swine herds, short incubation period (1˜2 days), morbidity rates between 10%˜100%, mortality rate in pigs between 10%˜100% (mortality rate in piglets can reach up to 100%), high fever in pigs after being infected (40° C.˜42° C., lasting for more than 3 days), dyspnea, diarrhea, wheezing, coughing, sneezing, hind limb paralysis, dog sitting, suddenly falling down, convulsions, lying on their sides, opisthotonus, making strokes with their arms, and finally dying of exhaustion, and the infection also can cause reproductive disorder symptoms such as declined semen quality of boar, as well as abortion of pregnant sow (the abortion rate can reach up to 35%), premature birth, stillbirth, weakened piglets (weakened piglets die by 14 days of age), etc. By means of prior art, vaccinated pigs cannot completely resist attacks by the wild virus, and still have symptoms like high fever, depression, partially or completely loss of appetite, with a infection rate of more than 30% and a mortality rate between 10% and 20%. According to literatures in the prior art, for example, Jin-mei Peng, et al., Identification and antigenic variation of new epidemiology of pseudorabies virus from swine. Chinese Journal of Preventive Veterinary Medicine, 2013, 35(1):1-4; Tong Wu et al., Identification and Characterization of a pseudorabies virus isolated from a dead piglet born to vaccinated sow. Chinese Journal of Animal infectious diseases, 2013, 21(3):1-7; Yu et al., Pathogenic Pseudorabies Virus, China, 2012. Emerging infectious Diseases. 2014, 20(1):102-104; An et al., Pseudorabies virus variant in Bartha-K61-vaccinated pigs, China, 2012. Emerging infectious Diseases. 2013. 19(11): 1749-1755, there is no vaccines capable of solving the pseudorabies caused by variant strains of porcine pseudorabies virus in the prior art.
The Chinese patent application CN103756977A has disclosed a gE and gI deleted variant strain of porcine pseudorabies virus, PRV-ZJ011G strain (of which the accession number is CGMCC No. 7957) and a vaccine prepared therefrom, of which the content of virus prior to being inactivated is 106.0TCID50. Immunization with said vaccine could provide a 100% protection rate for 5 healthy piglets at 45 days of age. Said patent application, however, cannot successfully provide an attenuated live vaccine against new PRV strains, due to both humoral and cellular immunity resulted from proliferation of attenuated live PRV vaccine in vivo.
The Chinese patent application CN103981153A has disclosed the construction of a gene deleted variant strain of the pseudorabies virus labeled with two fluorescent markers, wherein a variant strain of pseudorabies virus with deletion of gE, gI, US9 and TK gene is inserted with GRP gene and RFP gene as labels at the site of deleted genes through homologous recombination. Whereas in this patent application said a gene deleted variant strain is used as a vector of antigen, we don't know if it has immunological competence itself, or how strong the virulence of the variant strain is, since there are more than 70 gene fragments for pseudorabies virus.
It has been disclosed by Chun-Hua Wang et al. (Chun-Hua Wang, Jin Yuan, Hua-Yang Qin, et al, A novel gE-deleted pseudorabies virus (PRV) provides rapid and complete protection from lethal challenge with the PRV variant emerging in Bartha-K61-vaccinated swine population in China, Vaccine 32 (2014)3379-3385) that 6-week-old piglets injected with PRVTJ-gE− live vaccines got a complete protection from challenge and didn't exhibit fever. Whereas as is known to those skilled in the art, the virulence of the PRV live vaccines depends on the age of piglets. Also according to the general experience in the art, the vaccines may not be safe for 7-day-old piglets even though they are safe for 6-week-old piglets. The live vaccines may spread among pigs, therefore the vaccine which is only safe for 6-week-old piglets cannot be ensured to be used clinically and a live vaccine which is safe for 7-day-old piglets, is required in the prior art to prevent effectively infection with the new variant strains of PRV.